Even though there are 16 sets, the number of active sets are 2 and all others are empty or not active. I have seen, the working set is directly proportional to the number of DB_WRITER_PROCESSES, but not confirmed.

You can join x$bh.set_ds = x$kcbwds.addr to associate the buffer cache blocks to the working set.

In linux, starce -p <pid> produces follwoing trace. io_submit is the function call used to request for asychornus I/O and io_getevents is checking the response or completion queue for an asychornus I/O. While pwrite is DIRECTIO.